Question: Which of these numbers is prime? ${7,\ 42,\ 65,\ 87,\ 95}$
Answer: A prime number has exactly two factors: 1 and itself. The factors of 7 are 1 and 7. The factors of 42 are 1, 2, 3, 6, 7, 14, 21, and 42. The factors of 65 are 1, 5, 13, and 65. The factors of 87 are 1, 3, 29, and 87. The factors of 95 are 1, 5, 19, and 95. Thus, 7 is a prime number.